Antenna with built-in filter

Abstract

At least one filter block (25, 35, 45) is formed in a thin and flat dielectric multilayer structure (21) and fixed with radiation elements (2, 3). Each filter block includes at least one of a low-pass filter, a high-pass filter and a band-eliminating filter. On the surface (one major surface) side and / or the side face of the multilayer structure, at least one radiation element (2, 3) being connected with the filter block is provided and feeding parts (28, 38, 48) for supplying signal to the radiation elements are provided on the rear surface of the multilayer structure. Consequently, the antenna and the filter block are integrated and a small surface mountable antenna with a built-in filter of a structure such that signals are not mixed each other even when signals of a plurality of frequency bands are transmitted / received can be obtained.

Description

[0001]This application is the National Phase of International Application PCT / JP02 / 01637 filed Feb. 22, 2002.TECHNICAL FIELD[0002]The present invention relates to an antenna with a built-in filter which has a filter having a superior separating function so as not to generate a noise on another signal because of reciprocal interference even when a plurality of frequency bands are transmitted or received at the same time, and which is small in size so as to be suitable for being mounted on a portable telephone, a personal digital assistant or the like, and in which matching is easy. More particularly, it relates to an antenna with a built-in filter having a compact structure in which reciprocal interference will not occur even if it is constituted such that signals of a plurality of frequency bands such as cellular and GPS or Bluetooth can be transmitted or received by one block of antenna.BACKGROUND ART[0003]Conventionally, signals transmitted or received by an antenna pass through a...

AI Technical Summary

Benefits of technology

[0020]According to this structure, there can be provided the filter which passes a desired frequency band by combining the high-pass filter and low-pass filter, for example and its band width can be freely set. In addition, if necessary, a specific frequency band can be removed and only a desired frequency band can be passed. Furthermore, since the radiation element is fixed to the dielectric multilayer structure and it is directly connected to the filter, impedance between them can be matched easily, connection wiring is short, and loss can be considerably reduced, whereby there is provided the antenna with the built-in filter with high efficiency.

[0033]The dielectric multilayer structure according to the present invention is the dielectric multilayer structure in which the plural dielectric sheets each having an electroconductive film thereon are laminated and fixed, in which electroconductive films provided on upper and lower sides of a dielectric sheet are connected and a shield wall is formed in the dielectric multilayer structure in its thickness direction by forming a band-shaped via contact in the dielectric sheet. According to this constitution, even in the multilayer structure in which the electroconductive film is formed on the dielectric sheet, the electroconductive films can be connected through the ceramic (dielectric) sheet with low resistance and it can be completely shielded in the horizontal direction of the ceramic sheet. As a result, a high-performance circuit element which is compact in configuration and will not be subjected to the reciprocal interference, is obtained.

Problems solved by technology

However, a signal transmission path is locally narrowed in the connection using the through-hole, which increases high-frequency resistance or inductance and comes to increase in transmission signal loss or decline in the damping characteristic.

Although the structure can be shielded in the vertical direction by providing an earth conductor film on the ceramic sheet, the shielding is not effective in the surface direction of the multilayer structure (in the direction parallel to the ceramic sheet) because an electric wave is leaked laterally from a gap of the connecting parts of the through-hole.

However, since further miniaturization is demanded in the portable device, to provide the antennas at various places in the portable device is contrary to the demand for the miniaturization.

As described above, according to the conventional antenna with a built-in filter, since the antenna and the band pass filter are connected through the connector and connection cable, the device becomes large and loss is increased.

In addition, since the radiation element and the filter separately function, it is necessary to match the impedance of the radiation element, which further increase its size.

However, if such different type filters are manufactured at the same time, since the manufacturing steps are different, the cost is increased and a size is increased because of the mono-block structure.

Furthermore, according to the above-described band-pass filter, as the frequency band is increased, the shielding characteristic deteriorates, and there can not be provided a broadband band-pass filter having superior shielding characteristic.

In addition, as described above, if the antennas for the plural frequency bands have integrally the filter built-in, it means that the radiation elements for the plural frequency bands such as cellular and GPS or BT and the band-pass filter are arranged together at one place, they are interfered with each other or the signal of another frequency band could be mixed in.

However, there is a case where the antennas for cellular, GPS and Bluetooth are used at the same time, which could cause the reciprocal interference and lower the antenna performance.

Especially, the band-pass filter passes spurious which is an integral multiple of the frequency of the signal to be passed so that a noise is likely to enter.

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